The present invention relates generally to a central plant that includes multiple subplants configured to serve the heating loads and/or cooling loads of a building. The present invention relates more particularly to systems and methods for coordinating HVAC equipment staging across multiple subplants of a central plant.
A central plant typically includes various types of HVAC equipment configured to serve the thermal energy loads of a building or campus. For example, a central plant may include heaters, chillers, heat recovery chillers (HRCs), cooling towers, or other types of HVAC equipment. The central plant may consume resources from a utility (e.g., electricity, water, natural gas, etc.) to heat or cool a working fluid that is circulated to one or more buildings or stored for later use (e.g., in thermal energy storage tanks) to provide heating or cooling for the building.
Some central plants include multiple subplants (e.g., a heater subplant, a HRC subplant, a chiller subplant, etc.), each of which is configured to serve a particular type of load (e.g., heating, cooling, hot water, cold water, etc.). For example, a cooling load can be met by activating the chillers in the chiller subplant and/or the HRCs in the HRC subplant. Equipment staging within a subplant (e.g., activating or deactivating HVAC devices) is typically controlled by a subplant level controller configured to manage the equipment within the subplant. The subplant level controllers often operate independently and do not consider the state of any other subplant when determining whether to stage their equipment.
Some types of HVAC equipment consume more energy when they are initially started or activated than they do under steady-state operation. For example, chillers and HRCs may cause a temporary spike in energy consumption when they are initially started or activated. In some instances, an increase in cooling load may cause the load setpoints for the HRC subplant and the chiller subplant to increase simultaneously. However, if the chillers and the HRCs are staged at the same time, the resultant spikes in energy consumption can stack on top of each other, causing a high peak energy consumption.
A demand charge is a cost imposed by a utility provider based on the maximum usage of a particular resource (e.g., maximum energy consumption) during a demand charge period. A high peak energy consumption may be undesirable since it increases the maximum rate of energy consumption used by the utility provider to calculate the demand charge. However, it can be difficult and challenging to avoid spikes in energy consumption while ensuring that the heating and cooling loads are met in an energy efficient manner.